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Old 01-04-2013, 01:45 AM   #29
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Yes the best "Bang for buck" is GC-2 Golf Car batteries (These are six volt so you need pairs of them (Even numbers) with each pair wired in series to make one BIG!! 12 volt battery, roughly equal to an 8-D)

However they are also flooded wet cell type, and the O/P Was looking at AGM.. AGM is a Maintence free design, There are (in many cases) Very good reasons for wanting Maintence Free designs.
I agree with this post.
Plus the AGM batteries can be mounted almost anywhere in the coach without worrying about gas and acid spills. I am buying 4 to 6 AGMs as backups for my rig and a small generator to charge them. I can install them in our large utility area safely. This solution beats the 5k that an Onan Marquis 5500 with installation will cost. A reliable Honda EU200 should be fine, maybe 2 connected if needed. We are full-timers in a 40' KZ Escalade and our power goes out for short times in the winter....we also have a full-size residential fridge which I will put on an inverter.
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Old 01-04-2013, 01:50 AM   #30
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Woodglue

The wife uses a 12v CPAP every night for 8 hrs....
How cool, I did not know they made a 12v CPAP.

I love my CPAP.....but it's not 12V. Would you mind sending me that information when you get a chance.

Thanks
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Old 01-04-2013, 10:14 AM   #31
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Virtually all C-PAP machines are 12v DC. That brick in the cord converts 120v AC to 12v DC. c-pap.com has 12v cords for most machines. I got one for my Resperonics System One Auto from them. You could make your own with a plug from Radio Shack that fits your machine. I mounted a power plug socket (cigarette lighter) on my side of the bed frame and found a always hot 12v source under the bed. My cord came with a power plug.

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Old 01-04-2013, 12:11 PM   #32
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If you are hooking up 12 volt batteries you can use 1,2,3,4,5,6,7, 200, 1,000 however many you can carry without overloading your RV, in parallel,

Connected positive to positive, negative to negative.

The result, electrically, is one VERY BIG 12 volt battery. (And one very thin wallet if you are using AGM's).
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Old 01-05-2013, 10:33 AM   #33
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Woodglue,

You say you understand computers but not batteries, well, here is an analogy for you. You know the way you cannot count on the multiple of processors doing a distributed process and returning at the same time?
SAME - Same here.

If you put those three batteries in parallel, you will not get capacity * 3. If you are lucky, you might be able to count on capacity *2.5. I would explain why at great length, but I get paid to do that and I don't expect a check from the forum. Suffice it to say that one battery will want to be the hero of any charge cycle.

If you were a client, I would suggest that we look at two 6V-220 AH golfcart batteries in series. A pair of Lifeline(tm) that fit that bill may also be less expensive than your current choice.

You also need to get to work on a electric power audit. Use a spreadsheet and figure out just how many ampere-hours you really need.
most laptops (I haven't looked up yours) are about 5amps at 12V. That comes out to 120Ah per day. That is more than half your power right there and a good rule with lead-acid batteries is to avoid running them below 50% as that reduces the usable life.

I have done work on performance and long passage cruisers for years. I am advising you to do more research before you even buy wire.

Thinking is most cost effective thing you can do.

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Old 01-05-2013, 11:38 AM   #34
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Sorry for my ignorance, but if I use 4 6v batteries rated 220AH, am I going to get 440 or 880 Ahs?

I have an oxygen concentrator that will run all night, takes 325 watts. I would also use it sometimes during the day. I have an IPad, a laptop, a portable oxygen concentrator that has batteries that need to be recharged. PLUS, all the stuff, LED tv, radio, satellite receiver, etc.
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Old 01-05-2013, 12:53 PM   #35
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440, (When you pair the six volt batteries, in series, to make a 12 volt battery you add voltage.. Each pair, becomes in effect one BIG 12 volt battery.... When you pair the two 12 volt batteries in parallel you add amp hours making one even bigger 12 volt battery.

However, You get even more due to an effect I can't spell.

A common myth about unequal batteries in parallel is that one will "hog" all the charging current, and/or provide all the load current. Another is that one will "Fill up and signal the charger FULL before the other is full up.

Batteries will provide and accept current in accordance with their ability.

And the converter won't switch to FLOAT till the last battery gets full.
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Old 01-05-2013, 03:17 PM   #36
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Sorry for my ignorance, but if I use 4 6v batteries rated 220AH, am I going to get 440 or 880 Ahs?

I have an oxygen concentrator that will run all night, takes 325 watts. I would also use it sometimes during the day. I have an IPad, a laptop, a portable oxygen concentrator that has batteries that need to be recharged. PLUS, all the stuff, LED tv, radio, satellite receiver, etc.
The 4 6v batteries hooked up right lwill give you 12 v and 440 Ahs.
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Old 01-05-2013, 04:33 PM   #37
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Talking

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Originally Posted by Davdeb1 View Post
Sorry for my ignorance, but if I use 4 6v batteries rated 220AH, am I going to get 440 or 880 Ahs?

I have an oxygen concentrator that will run all night, takes 325 watts. I would also use it sometimes during the day. I have an IPad, a laptop, a portable oxygen concentrator that has batteries that need to be recharged. PLUS, all the stuff, LED tv, radio, satellite receiver, etc.

440AH

You have two 6V batteries in series which provides 12V @ 220AH and this is connected in parallel with two additional 6V batteries in series providing 12V and another 220AH for a total of 440AH @ 12V.

With batteries, series connections increase system voltage and parallel connections increase capacity.
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Old 01-05-2013, 06:22 PM   #38
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For practical purposes, we've found that four 6v Trojan batteries (440 Ah) is enough for full-time living. Running 2 laptops for 3-8 hours a day and watching a movie on a 26" TV at night plus nighttime lights, we use about 100-120 Ah per day. Our RV fridge is propane.

On our boat, which has a DC fridge, using the laptops the same amount but with a smaller TV (22" versus 26"), we use about 120-160 Ah per day. That setup has four 4D AGM batteries (640 Ah).

The real key is being able to replace the 100-160 Ah that you've used up within the next day -- via solar or generator... the batteries are useless once they are depleted...

You need to size the batteries to cover a day or 2 of use...

You need to size your charging system to replace those amp-hours quickly... if solar, it should replace those amp-hours within one sunny day... if a generator, it should replace those amp-hours before you get tired of listening to it and paying for its fuel!!
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Old 01-05-2013, 06:34 PM   #39
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Davdeb1 -- I just re-read your post and am thinking about your 325 watt oxygen concentrator. If it's 325 watts, then it will burn ~27 amps per hour (325/12). Multiply that by your 8 hours of sleeping, and you will be out 216 amps from that one appliance while you are in dreamland.

That is a lot of amps. Typical daily life will probably consume another 100-140 amps in a 24 hour period. That's a total of 316-356. Call it 330 for simplicity.

The rule of thumb is to avoid depleting your batteries more than 30%. So you will need something along the lines of 1,000 amp-hours of battery capacity (3 times your daily usage of 330 amps).

Plan on either a bank of eight 6v batteries or a bank of four or five 4D (or even 8D) AGM batteries that have a capacity of 200 ah apiece (I believe the Lifelines are 200 ah per 4D battery). Also plan on a huge recharging system. If it were solar only, probably a total of 1000 watts would be a good idea...

I know this sounds like a mammoth system, but it's not that big compared to house systems or many boating systems we've seen where people have DC deep freezes on their boats and live in the tropics...
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Old 01-05-2013, 07:14 PM   #40
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One suggestio Groovy.. Inverters are not 100% efficient (geneally only 90) so I have found that it is easier when predicting amp hour draw. to think 10 volts.

For one, makes the arithmetic very easy

2: Takes care of inverter and line loss

3: Adds a tiny safety margain.
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Old 01-05-2013, 09:15 PM   #41
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Davdeb1 -- I just re-read your post and am thinking about your 325 watt oxygen concentrator. If it's 325 watts, then it will burn ~27 amps per hour (325/12). Multiply that by your 8 hours of sleeping, and you will be out 216 amps from that one appliance while you are in dreamland.

That is a lot of amps. Typical daily life will probably consume another 100-140 amps in a 24 hour period. That's a total of 316-356. Call it 330 for simplicity.

The rule of thumb is to avoid depleting your batteries more than 30%. So you will need something along the lines of 1,000 amp-hours of battery capacity (3 times your daily usage of 330 amps).

Plan on either a bank of eight 6v batteries or a bank of four or five 4D (or even 8D) AGM batteries that have a capacity of 200 ah apiece (I believe the Lifelines are 200 ah per 4D battery). Also plan on a huge recharging system. If it were solar only, probably a total of 1000 watts would be a good idea...

I know this sounds like a mammoth system, but it's not that big compared to house systems or many boating systems we've seen where people have DC deep freezes on their boats and live in the tropics...
500 lbs of batteries is way too much weight, plus finding the space for them. I guess I am going to have to use my portable oxygen concentrator. The transformer ac input is 100-240v-1amp. I will just have to restrict my use of the AC 300 watt concentrator to when I am plugged in somewhere. Even if I wanted to go solar, 1000 watts would be horrendously expensive, not to mention the cost of all those batteries.
The big concentrator puts out up to 5 liters continuous flow, while the portable only puts out a pulse flow which is about 1/2 that.
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Old 01-05-2013, 09:25 PM   #42
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Groovy, thank goodness you know this stuff. But I am curious, if I have 4 6v AGM that are rated 220 AH each, and that would only give me 440 AH. If 4 gives no more AH THAN 2 does, why would 8 give me more than 4? I know it's a dumb question, but doesn't make sense to me. Also, I have a 7500 watt Onan, how long would it take to replace 350 Ah back in the batteries?
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